Town of Robbinsville

Two 800,000-Gallon Biological Nutrient Removal (BNR) Tanks

The Town of Robbinsville, North Carolina’s old wastewater treatment plant (WWTP) was performing under capacity and was suppressing opportunities for growth in their community. They needed a new wastewater management system that would allow them to meet the current and future demands of commercial and residential developments.

The Town’s new WWTP provides just that. Thanks to funding from USDA Rural Development, the North Carolina Golden Leaf Foundation and the Appalachian Regional Commission, the new plant has a capacity of 630,000 gallons and was designed by McGill Associates to expand up to 850,000 gallons.

CROM has been longtime business partners with the folks at McGill Associates – and for good reason. Their team has decades of engineering experience in wastewater projects and can expertly manage and design wastewater management systems at any scale. Hickory Construction, the general contractor for this plant, has been serving the Carolinas for over 70 years.

The Robbinsville WWTP provides for the removal of nitrogen and phosphorous per the discharge limits set by the North Carolina Department of Environment and Natural Resources, ultimately preserving the water quality of the nearby Cheoah River and Santeetlah Lake. The two BNR tanks built by CROM require interior hydrostatic walls to segment the different treatment processes – aeration, clarification, digestion and equalization. Hydrostatic simply means that when one compartment is full of water and the one next to it is empty, the wall must be able to withstand the pressure of the water pushing against it.

Early CROM BNR tanks were built with shotcrete interior hydrostatic walls. This proved to be cumbersome and somewhat expensive, so the majority of these tanks were built by steel tank manufacturers. In 1995, CROM engineers developed a design where the customer could specify the superior CROM prestressed tank. Our engineers worked closely with the process equipment manufacturer who provided the steel interior components. CROM would encapsulate steel I-beams in the concrete floor which is then welded to the steel walls. The first installation proved successful and with a few improvements in the design, we now proudly offer this type of tank to consulting engineers, communities and utilities who recognize the advantages of a CROM Prestressed Concrete Tank.

For a look at projects similar to the Robbinsville WWTP, take a look at the Marion County Utilities WWTP and the Ave Maria Utilities Wastewater Treatment Tank.

CROM Shotcrete
Shotcrete History and Use: Part One of the Shotcrete Series

Early Beginnings

In 1942, J.M. Crom Sr. first wrapped high-strength wire in a continuous spiral on the exterior of cylindrical concrete tanks. The “wrapping” method tensioned the prestressing wire before it was placed on the wall,…

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